It's a fight that has ended up in San Francisco federal court. The opening arguments took place on Friday morning, and it could turn out to be a landmark copyright case.

The movie industry says it makes $20 billion a year selling DVDs. What they're worried about is losing that business to a practice known as 'rent, rip and return.'

Go to a video store, rent a movie, load it into your computer and burn a permanent copy of the movie onto your hard drive. Real Networks has developed a program that would allow you to do that, though you can't buy it because it's tied up in the lawsuit.

"Well, we do all we can to discourage that kind of behavior and conduct. Frankly, there are a lot of reasons why our product would not be the one you would use if you frankly want to do something inappropriate," said Bob Kimball, general counsel for Real Networks.

Kimball says the company just wants to give DVD owners fair use of the DVDs they buy by being able to make a backup copy.

"We don't allow those DVD backup copies we make to be distributed out on the Internet or to be further copied," said Kimball.

But keeping any permanent copy from a movie you rent is stealing says Mark Greenberg, professor of law at Golden Gate University.

"This is really akin to going into a store, picking up a quart of milk and walking out with it," said Greenberg.

But it's not that cut and dry at LeVideo store in San Francisco.

"The way I look at it as a consumer or person who is watching movies, media is becoming more free and on the Internet," said customer Marianna Whang.

Whang says selling stolen copies would be wrong, but just ripping off a copy and watching it occasionally wouldn't bother her.

"There's no question that in the hearts and mind battle Hollywood has kind of lost the battle with respect to a younger generation that basically doesn't see anything wrong with making unauthorized copies, distributing them freely," said Greenberg.

The lawyer for Real Networks says that's really not what this lawsuit is about. It's about the movie industry wanting to get into Real Network's business.

"They're coming out with products that do essentially exactly what our product does. That's exactly what they're doing," said Kimball.

The lawyers for Hollywood did not respond to ABC7's request for an interview. They argued the press should be barred from some parts of the trial because trade secrets could be disclosed.

The same judge that shut down Napster is hearing this case in federal court.